In the air distribution system for a typical large modern building, accurate and reliable control of various dampers (air valves) is essential to the proper functioning of the system. Many large buildings are currently constructed as sealed units, having an air distribution system which includes a central source that provides conditioned return air which can be mixed with a percentage of outside air. The mixture is then circulated through the building.
Under certain circumstances, it may be desirable to draw a large quantity of outside air for mixing with conditioned and return air from the building. However, at other times no outside air is needed. Under these conditions, and others within a building, a damper capable of tightly closing off the air passage is desirable.
The prior art contains several approaches to achieving control with a damper of this kind, and Canadian Pat. No. 1,143,992, issued Apr. 5, 1983 to Mitco Corporation, is exemplary.
However the latter patent and others are based on quasi-parallelogram linkages and require members of a substantial size for the necessary rigidity.